Evaporating or evaporated fuel leaking to atmosphere from a fuel tank or a float chamber in a carburetor contains considerable hydrocarbons and is one of the causes for air pollution. Also, it is a cause for fuel loss. Various types of technology have been introduced to prevent evaporating fuel leakage to the atmosphere. One of the representative technologies for that purpose involves absorbing and storing evaporating fuel in a fuel tank in a canister, which contains absorbent such as activated carbon, when the engine is not operative and then purging and feeding the evaporating fuel absorbed by and stored in the canister to the engine when it is running.
This type of evaporating fuel control device for vehicles is disclosed, for instance, in Japanese Patent Laid Open Publication 17354/1987. The fuel vapor discharge blocking apparatus disclosed in this patent publication has a canister arranged to collect evaporating fuel generated in a fuel tank, a first path means having a relatively large path area and a second path means having a relatively small path area, each connected in parallel to a suction system of an engine. Valve means selectively communicates one of the first and second path means. Temperature detecting means detects fuel temperature and communicates the suction system of the engine to the first path means when temperature of the fuel is higher than a previously specified value, to the second path means when temperature of the fuel is lower than a previously specified value, and to the first path means only for a specified period when the temperature of the fuel detected when the engine is restarted is lower than temperature of the fuel detected when the engine is shut off and the temperature detected and remembered by the temperature detecting section is lower than the previously specified value.
Also, another example of an evaporating fuel control device is disclosed in Japanese Patent Laid Open Publication 20669/1987. The disclosed fuel evaporating vapor discharge blocking apparatus has a running state detecting means for detecting the running state of a combustion engine, an evaporating gas path to introduce a fuel evaporating gas into a fuel tank, and a variable control means for flexibly controlling a path area of the evaporating gas path according to the running state of the engine, and controlling the path area of the evaporating gas path according to a fuel feed rate to the combustion engine or a relative number of rotations previously set for the idling state.
Another example of an evaporating fuel control device is disclosed in Japanese Patent Laid Open Publication No. 243957/1987. The disclosed method of controlling fuel feed when a combustion engine is started is based on a system having an electro-magnetic valve arranged to open or close a communicating path which communicates a canister to an intake air path in the downstream of a throttle valve. The system prevents leaning of mixed air fed to the engine by determining whether the engine is started under high fuel temperature or not and opening the electro-magnetic valve to discharge evaporating fuel from the canister to the intake air path.
In conventional types of evaporating fuel control devices, as shown in FIG. 9, a duty percent is calculated, for instance, from a base map comprising an engine speed, Ne, and a load. A purge control valve arranged in an air path between a canister and an intake air path is opened or closed according to the duty percent for controlling a rate of purging evaporating fuel.
In the evaporating fuel control devices as described above, however, a quantity of hydrocarbons (HC) generated from a fuel tank increases, for instance, when an engine is run under high temperature in summer.
As a result, hydrocarbons (HC) absorbed in the canister cannot be purged fully because the rate of purging evaporating fuel is adjusted to the same level as that under the normal temperature, and performance of the canister goes down. This situation is disadvantageous for practical operation, and also a large quantity of hydrocarbons (HC) may be released from the canister to atmosphere.
An object of the present invention is to solve the problems described above.